Flash memory is a non-volatile memory capable of maintaining the contents of information even without an external power supply, and thus the flash memory can achieve a data storage without the need of consuming electric power, and the flash memory also has the advantages of a repeated write and read function, a small size, a high capacity, and a convenient portability, so that the flash memory is particularly suitable to be applied to portable devices. In addition to its current application provided for computer motherboards to store BIOS data, NOR flash memory is also used extensively in mobile phones and other handheld devices for storing system data, and its high access speed can satisfy the booting requirement of the handheld devices.
As the development of semiconductor process advances rapidly, the capacity of memory increases constantly, the semiconductor process becomes increasingly more difficult, and the limitations of physical phenomena also become more significantly. Thus, manufacturers and designers spare no effort to find a procedure or a method to improve the yield rate of memories.
Since a drain junction is one of the major factors of producing a defect of a NOR flash memory device, therefore a metallization process is generally performed to enhance the performance of the memory device. In other words, a self-aligned silicidation deposits a metal silicide layer onto a drain area to reduce the contact resistance and allow current to pass through the metal silicide layer having a lower resistance first and then enter into the drain area. The metal silicide layer must come with a specific depth in the drain junction in order to reduce the contact resistance, and thus a loss at the drain junction will be produced when the metal silicide layer is formed, and the loss will increase a current leak of the drain junction.
Since the ion implantation of a source/drain area relates to the electric properties of the memory device directly, therefore the design of the memory device tends to be optimized, and it is necessary to control the best condition for the energy and dosage of the ion implantation to lower the defective rate and improve the yield rate of the memory device.